Method and system for enhancing bass effect in audio signals

ABSTRACT

The quality of music output from audio systems is improved by simulating the effect of low frequency signals in the human ear. This thus allows listeners to perceive the lower frequency signals, even though the speakers may be incapable of providing such low frequency outputs. Method and systems provided for processing enhancing bass effect in audio signals. Said method and systems result in the bass enhancement being computationally less intensive. The bass effect enhancement techniques described are based on the response of sine and cosine transfer functions and on the directional independence of low frequency components. The human ear is unable to resolve directions from low frequency components. The bass effect enhancement technique alternatively is based on response of an exponential transfer function.

PRIORITY CLAIM

This application is a divisional of U.S. application Ser. No. 11/280,952filed Nov. 16, 2005, which claims priority from Singapore PatentApplication No. 200407881-2 filed Dec. 31, 2004. Said applications arehereby incorporated by reference in their entirety.

TECHNICAL FIELD

The invention disclosed relates to a method and system for enhancingbass effect in audio signals. In particular, this invention relates to amethod and system for enhancing bass effect of audio signals using lowcomplexity non-linear saturating functions.

BACKGROUND

There have been many methods proposed for enhancing perception of basscontent of audio signals. These methods vary from enhancing a certainband of frequencies to using amplitude modulation. Almost all of thesemethods are based on either temporal theory or place theory of pitchperception.

One method of bass enhancement generates consecutive harmonics for lowfrequency content of audio signals. Harmonic signals generated aremodified according to a psycho-acoustic model and are output to thespeakers. In this method, loudness modeling of the ear is used foradjusting amplitudes of the harmonics to match amplitude of the lowfrequency signal.

Another method of bass enhancement generates only even harmonics of thelower frequencies and a band of frequencies just above this bassfrequency is enhanced to give a better bass effect.

Yet another, is based on the amplitude modulation of a carrier wave bythe low frequency content of the audio signal. There is also a methodbased on generating frequency components such that the differencebetween adjacent partials approximates the frequency of the lowfrequency signal.

With advances in audio technology, audio systems are now not only ableto reproduce music but also provide various audio-modes to listeners forlistening to effects they desire. These audio-modes are helpful increating musical effects the listeners want on the output of their audiosystems. In some of these audio systems, there are options provided forspecifically enhancing bass effect on the music. In this mode the systemis expected to boost the bass frequency content of the system.

Some of the audio speakers of these audio systems are not able toreproduce low frequency spectrum efficiently. This is because of thelimitation in size and other constraints of the audio speakers. As aresult some of these audio systems, attenuate frequencies below 120 Hz.However, this disadvantageously prevents these audio systems fromreproducing music effectively. In particular, some musical instrumentsexamples of which are: drums and pianos have frequency components below120 Hz.

Therefore, a need clearly exists for a method and system for enhancingbass effect of audio signals that overcome the problems or at leastalleviate the limitations of existing systems.

SUMMARY

A method and system are provided for enhancing bass effect in audiosignals using low complexity non-linear saturating functions.

Accordingly, provided herein is a method for enhancing bass effect ofaudio signals, the audio signals having a first input channel and asecond input channel, comprising: extracting low frequency components ofthe first input channel and the second input channel; passing the lowfrequency components of the first input channel through a sine wavetransfer function to produce a first output signal; passing the lowfrequency components of the second input channel through a cosine wavetransfer function to produce a second output signal; filtering the firstoutput signal and the second output signal by a band pass filter toproduce a band filtered first output signal and a band filtered secondoutput signal; adding the band filtered first output signal to the firstinput channel producing a resultant first output signal; and adding theband filtered second output signal to the second input channel producinga resultant second output signal. The extracting of low frequencycomponents of the first input channel and the second input channel mayproduce low frequency components of the first input channel and thesecond input channel. The resultant first output signal and theresultant second output signal may be input to stereo speakers. Duringfiltering, the first output signal and the second output signal may belimited to a predetermined frequency range. The sine wave transferfunction is generally represented by (i)=sin(x(i)), where x is the inputsignal, which is normalized, and y is the output normalized signal. Thecosine wave transfer function is generally represented byy(i)=cos(x(i)), where x is the input signal, which is normalized, and yis the output normalized signal. Adding the band filtered first outputsignal to the first input channel further comprises extracting highfrequency components of the first input channel and adding the highfrequency components to the band filtered first output signal. Addingthe band filtered second output signal to the second input channel mayfurther comprise extracting high frequency components of the secondinput channel and the adding the high frequency components to the bandfiltered second output signal. Extracting may further comprisesattenuating the low frequency components of the first input channel andthe second input channel.

In addition, provided herein is a system for enhancing bass effect ofaudio signals, the audio signals having a first input channel and asecond input channel, comprising: a first low pass filter configured toreceive signals from the first input channel; a second low pass filterconfigured to receive signals from the second input channel; a sinefunction block coupled to an output of the first low pass filter andconfigured to produce a first output signal; a cosine function blockcoupled to an output of the second low pass filter and configured toproduce a second output signal; and a band pass filter configured tolimit the frequency range of the first output signal and the secondoutput signal and produce a filtered first output signal and a filteredsecond output signal. The system may further comprise a high pass filterfor extracting high frequency components of the first input channel andthe second input channel. The extracted components may be added to thefiltered first output signal and the filtered second output signal. Thesystem may further comprise an input source for receiving the first andsecond output signal. The input source may be stereo speakers. Thesystem may further comprise an attenuator for attenuating the lowfrequency components of the first input channel and the second inputchannel.

Also disclosed is a method for enhancing bass effect of audio signals,the audio signals having a first input channel and a second inputchannel, comprising: extracting low frequency components from the firstinput channel; extracting low frequency components from the second inputchannel; passing the low frequency components of the first input channelthrough a sine wave transfer function; passing the low frequencycomponents of the second input channel through a cosine wave transferfunction; bandpass filtering the first output signal to produce a bandfiltered first output signal; bandpass filtering the second outputsignal to produce a band filtered second output signal; adding the bandfiltered first output signal to the first input channel producing aresultant first output signal; and adding the band filtered secondoutput signal to the second input channel producing a resultant secondoutput signal. Adding the band filtered first output signal to the firstinput channel may further comprise extracting high frequency componentsof the first input channel and adding the high frequency components tothe band filtered first output signal. Adding the band filtered secondoutput signal to the second input channel may further compriseextracting high frequency components of the second input channel and theadding the high frequency components to the band filtered second outputsignal. Extracting low frequency components from the first input channelmay further comprise attenuating the low frequency components of thefirst input channel. Extracting low frequency components from the secondinput channel may further comprise attenuating the low frequencycomponents of the second input channel. The sine wave transfer functionis represented by y(i)=sin(x(i)), where x is the input signal which isnormalized; and y is the output normalized signal. The cosine wavetransfer function is represented by y(i)=cos(x(i)), where x is the inputsignal which is normalized; and y is the output normalized signal.

Also provided is a system for enhancing bass effect of audio signals,the audio signals having a first input channel and a second inputchannel, comprising: a low pass filter configured to receive the firstand second input channels and extract low frequency components of thefirst and second input channels; a circuit operable to pass each of thelow frequency components of the first and second input channels througha sinusoidal wave transfer function to produce a first output signal anda second output signal; a band pass filter configured to limit frequencyrange of the first output signal and the second output signal to apredetermined frequency range and respectively produce a band filteredfirst output signal and a band filtered second output signal; a mixerconfigured to add the band filtered first output signal to the firstinput channel; and a mixer configured to add the band filtered secondoutput signal to the second input channel. The circuit may include asine function block for receiving low frequency components of the firstinput channel and producing the first output signal and a cosinefunction block for receiving low frequency components of the secondinput channel and producing the second output signal. The sine functionblock is represented by y(i)=sin(x(i)), where x is the input signalwhich is normalized; and y is the output normalized signal. The cosinefunction block is represented by y(i)=cos(x(i)), where x is the inputsignal which is normalized; and y is the output normalized signal. Thesystem may further comprise at least one a high pass filter adapted toextract high frequency components of the first input channel and thesecond input channel before addition to the band filtered first outputsignal and the band filtered second output signal. The system mayfurther comprise at least one attenuator adapted to attenuate the lowfrequency components of the first input channel and the second inputchannel.

Still further is provided a method for enhancing bass effect of audiosignals, the audio signals having input channels, comprising: extractinglow frequency components from the input channels, wherein content ofeach input channel is not independent; passing extracted low frequencycomponents through sinusoidal wave transfer functions; filtering theextracted low frequency components; mixing the extracted low frequencycomponents; wherein for each input channel operations are performedseparately. The extracting includes low pass filtering each inputchannel separately. Mixing comprises separately mixing filtered outputof each input channel with original signals feeding into each inputchannel. During operation output from each input channel remainsseparate. The method further comprises providing resultant outputsignals to input channels of at least one audio speaker. Generally,extracting low frequency components from each input channel occurssimultaneously. The input channels are generally stereo channels. Thesinusoidal wave transfer functions include a sine wave transfer functionfor at least a first input channel and a cosine wave transfer functionfor at least a second input channel.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be more fully described, by way of example, withreference to the drawings of which:

FIG. 1 illustrates a functional block diagram of a system according to afirst embodiment;

FIG. 2 illustrates a functional block diagram of a system according to asecond embodiment;

FIG. 3 illustrates a functional block diagram of a system according to athird embodiment;

FIG. 4 illustrates a functional block diagram of a system according to amono version of the third embodiment;

FIG. 5 illustrates a frequency plot of an input signal having a 50 Hzfrequency component;

FIG. 6 illustrates a frequency domain plot of a resultant first outputsignal of the first and second embodiment having an input as shown inFIG. 5;

FIG. 7 illustrates a frequency domain plot of a resultant second outputsignal of the first and second embodiment having an input as shown inFIG. 5;

FIG. 8 illustrates a frequency domain plot of an input signal having a50 Hz and 70 Hz frequency component;

FIG. 9 illustrates a frequency domain plot of a resultant first outputsignal of the first and second embodiment having an input as shown inFIG. 8;

FIG. 10 illustrates a frequency domain plot of a resultant second outputsignal of the first and second embodiment having an input as shown inFIG. 8;

FIG. 11 illustrates a frequency domain plot of an input signal having 50Hz and 75 Hz frequency components; and

FIG. 12 illustrates a frequency domain plot of a resultant output signalof the third embodiment having an input as shown in FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

In the following description, details are provided to describeembodiments of the invention. It shall be apparent to one skilled in theart, however, that the embodiments may be practiced without suchdetails. Some of these details may not be described at length so as notto obscure the preferred embodiments.

The embodiments can be used to improve the quality of music output fromaudio systems by simulating the effect of low frequency signals in thehuman ear. This thus allows listeners to perceive the lower frequenciessignals, even though the speakers may be incapable of providing such lowfrequency outputs. The embodiments provide simple methods for enhancingbass effect of audio signals for enhanced perception. The simple methodsalso result in the processing of bass content being computationally lessintensive.

Certain concepts pertaining to human hearing are further discussed toprovide background regarding the embodiments. They are: temporal theoryof human hearing, phenomenon of missing fundamental and the directionalindependence of low frequency components.

Temporal Theory of Human Hearing

The temporal theory of the human auditory system suggests that the pitchof a sound stimulus is related to the time pattern of the neuralimpulses evoked by that stimulus. Nerve firings tend to occur at aparticular phase of a stimulating waveform. Thus, time intervals betweensuccessive spikes approximate integer multiples of the period of thestimulating waveform. Pitch is thus related to the time pattern of thesenerve impulses. The temporal theory only applies to low frequencies andcannot work for frequencies above 4000 or 5000 Hz.

Thus when a complex sound waveform is exposed to the human ear;according to the temporal theory, the human ear will be able to perceivesounds of different pitches. These pitches might have been the result ofinteraction of several partials present in the complex sound signal. Thepitch associated with the complex sound waveform would be the one towhich attention is most strongly drawn by virtue of its loudness or ofits contrast with previous sounds.

Non-Linear Saturation

When an input waveform is passed through a block which saturates theinput in a gradual manner, an output waveform of this block will notonly have the original frequency, but will also contain other frequencycomponents. The frequency components present in the output waveformdepends on the frequencies present in the input waveform and theconfiguration of the saturating curve. The non-linear curve does nottreat the entire amplitude range in a similar way.

In other words, the gain of the curve depends on the amplitude range ofthe signal. Thus when an input waveform is normalized and passed througha block which does gradual saturation, it is equivalent to passing theinput waverform through a non-linear curve. This results in an outputwaveform, which has other frequency components which are directlyrelated to the frequencies present in the input waveform.

Directional Independence of Low Frequency Components

Low frequency components of music signals are found to have nodirectionality. This means that the direction from which the lowfrequency components of the music are coming from are not critical tothe human ear. This is likely due to the fact that human ears areseparated by a relatively short distance, resulting in the inability ofthe human brain to distinguish the direction from which the lowfrequency sound is coming from.

The bass effect enhancement described in several embodiments are basedon a response of sine and cosine transfer functions and on thedirectional independence of low frequency components. The human ear isunable to resolve directions from low frequency components. The basseffect enhancement described in an additional embodiment is based onresponse of a exponential transfer function.

First Embodiment

Referring to FIG. 1, a representative system 10 for enhancing basseffect in audio signals in accordance with a first embodiment is shown.The system 10 is applicable for stereo channels, as an example. Duringprocessing, the contents of the channels are performed separately. Thisassumes that the low frequency content in each of the channels are nottotally independent of each other.

The system 10 comprises low pass filters 18 for extracting low passfrequency components from at least a first input channel 15 a and atleast a second input channel 16 a. The at least two input channels beingstereo channels. The system 10 further comprises a sine function block20 and a cosine function block 22, both of which are coupled to bandpass filters 1. The resulting output of the bandpass filters 19, arerespectively added to at least the first input channel 15 a and/or thesecond input channel 16 a via one or more mixers 24.

In operation, the method for enhancing bass effect in audio signals ofthe first embodiment as represented by FIG. 1 starts with extracting lowfrequency components 15 b from the first input channel 15 a using thelow pass filter 18. The low-frequency components 15 b of the first inputchannel 15 a are passed through a sinusoidal wave transfer functions,such as sine function block 20. The sine function block 20 generates afirst output signal 15 c, having frequencies of which are dependent onthe signal frequencies of the first input channel 15 a.

The first output signal 15 c undergoes filtering by a band pass filter19. The band pass filter limits the frequency of harmonics from thefirst output signal 15 c to a predetermined frequency range to produce aband filtered first output signal 15 d. The band filtered first outputsignal 15 d is generally added to the original contents of the firstinput channel 15 a via mixer 24 producing a resultant first outputsignal 15 e. The resultant first output signal 15 e is sent as input toat least one of the stereo input channels of at least one audio speaker.

The second input channel 16 a is simultaneously and similarly processed.The method simultaneously extracts low pass frequency components 16 bfrom at least one second input channel 16 a using the low pass filter18. The low-frequency components 16 b of the at least one second inputchannel 16 a are passed through a sinusoidal wave transfer functions,such as cosine function block 22. The cosine function block 22 generatesa second output signal 16 c, having frequencies of which are based onthe signal frequencies of the at least one second input channel 16 a.

The second output signal 16 c undergoes filtering by the band passfilter 19. The band pass filter limits the frequencies present in thefirst output signal 16 c to a predetermined frequency range to produce aband filtered second output signal 16 d. The band filtered second outputsignal 16 d is generally added to the original contents of the secondinput channel 16 a via mixer 24 producing a resultant second outputsignal 16 e. The resultant second output signal 16 e is sent as input toat least one of the stereo input channels of at least one audio speaker.

As described, with a method of the first embodiment, the resultant firstoutput signal 15 e will, in one form, have the original contents of thefirst input channel 15 a together with the filtered output of thesinusoidal wave transfer function (e.g., sine function block 20 for FIG.1). The resultant second output signal 16 e will, in one form, have theoriginal contents of the second input channel 16 a of the input audiosignal together with the filtered output of the sinusoidal wave transferfunction (e.g., cosine function block 22 for FIG. 1). This provides anenhancement to the bass effect of the audio signals.

Second Embodiment

Referring to FIG. 2, a representative system 30 for enhancing basseffect in audio signals in accordance with a second embodiment is shown.The system 30 is basically applicable for stereo channels and the outputof the processing is at least a two channel audio output.

The system 30 similarly comprises low pass filters 18 for extracting lowfrequency components 15 b, 16 b from the first input channel 15 a andthe second input channel 16 a. The two input channels being stereochannels. The system 30 further comprises an initial mixer block 19, asine function block 20 and a cosine function block 22, both filtersbeing coupled to the band pass filters 18. The resulting output of thebandpass filters 18 are respectively added to the first input channel 15a and the second input channel 16 a via mixers 24.

In operation, the method for enhancing bass effect in audio signals ofthe second embodiment includes extracting low pass frequency components15 b, 16 b from the first input channel 15 a and the second inputchannel 16 a using the low pass filters 18. The low-frequency components15 b of the first input channel 15 a and the low frequency components 16b of the second input channel 16 a are added together in the initialmixer block 19, producing an initial audio stream 17.

The initial audio stream 17 is split into a first audio stream 17 a anda second audio stream 17 b.

The first audio stream 17 a is passed through the sine function block20. The sine function block 20 generates a first output signal 27 a, thefrequencies of which are dependent on the signal frequency of the firstinput channel 15 a.

The second audio stream 17 b is passed through the cosine function block22. The cosine function block 22 generates a second output signal 29 a,having frequencies of which are dependent on the signal frequency of thefirst input channel 16 a.

The first output signal further 27 a undergoes filtering by a band passfilter 19. The band pass filter limits the frequency of harmonics fromthe first output signal 27 a to a predetermined frequency range toproduce a band filtered first output signal 27 b. The band filteredfirst output signal 27 b is then added to the original contents of thefirst input channel 15 a via the mixer 24 producing a resultant firstoutput signal 27 c. The resultant first output signal 27 c is then sentas input to one of the stereo input channels of an audio speaker.

Simultaneously, the second output signal further 29 a undergoesfiltering by a band pass filter 19. The band pass filter 19 limits thefrequency of harmonics from the second output signal 29 a to apredetermined frequency range to produce a band filtered second outputsignal 29 b. The band filtered first output signal 29 b is then added tothe original contents of the second input channel 16 a via the mixer 24producing a resultant second output signal 29 c. The resultant secondoutput signal 29 c is then sent as input to one of the stereo inputchannels of the audio speaker.

In this method of the second embodiment, the resultant first outputsignal 27 c will have the original contents of the first input channel15 a along with the filtered output of the sine function block 20. Theresultant second output signal 29 c will have the original contents ofthe second input channel 16 a of the input audio signal along with thefiltered output of the cosine function block 22.

In both the first and second embodiment, the audio speakers will outputthe resultant first output signal 15 e, 27 c and the resultant secondoutput signal 16 e, 29 c. Since the human ear is unable to distinguishthe direction from which the low frequencies signals come from. Thecombination of the resultant first output signal 15 e, 27 c and theresultant second output signal 16 e, 29 c will provide an enhancement tothe bass effect of the audio signals.

Third Embodiment

The system and method of the third embodiment is utilizes the fact thata multiple tone wave passed through an exponential transfer functionresults in an output wave having multiple frequencies, which aremultiples of input frequencies as well as sum and difference componentsof the input sinusoidal frequencies and its harmonics. The combinedeffect of all these frequencies will give the same acoustical effect asthe original input wave to the system.

The bass effect enhancement method of the third embodiment may beapplied on both mono as well as stereo input signals. The thirdembodiment involves low pass filtering, passing through an exponentialtransfer function to generate harmonic frequencies and sum anddifference frequencies. A band pass filter is also used to limit therange of the frequency components.

Referring to FIG. 3, the representative system 60 of the thirdembodiment comprises low pass filters 18 for extracting low passfrequencies from a first input channel 15 a and a second input channel16 a. The two input channels being stereo channels. The system 60further comprises mixers 24 and an exponential function block 30, whichis coupled to a band pass filter 19. The resulting output of thebandpass filter 19 is split and added to the first input channel 15 aand the second input channel 16 a via the mixers 24.

In operation, the method for enhancing bass effect in audio signals ofthe third embodiment includes extracting low frequency components 15 b,16 b from the first input channel 15 a and the second input channel 16 ausing the low pass filters 18. The low-frequency components 15 b of thefirst input channel 15 a and the low frequency components 16 b of thesecond input channel 16 a are added together in a mixer 24, producing adown-mixed single audio stream 31.

The step of passing the down-mixed single audio stream 31 through theexponential function block 30 is performed to generate an output signal33.

The output signal 33 undergoes filtering by a band pass filter 19. Theband pass filter limits the frequency from the output signal 33 to apredetermined frequency range to produce a band filtered output signal35. The band filtered output signal 35 is then split into a first bandfiltered output signal 35 a and a second band filtered output signal 35b.

The first band filtered output signal 35 a is added to the originalcontents of the first input channel 15 a via a mixer 24 producing afirst resultant output signal 36. The second band filtered output signal35 b is added to the original contents of the second input channel 16 avia a mixer 24 producing a second resultant output signal 37.

The first resultant output signal 36 and the second resultant outputsignal 37 are sent as input to the stereo input channels of audiospeakers.

Referring to FIG. 4, the system 60 and method of the third embodimentmay be easily adapted for catering to mono input of audio signals. Thesystem 60 a for mono input of audio signals in accordance with the thirdembodiment comprises a single mono input channel 13 a, the exponentialfunction block 30 coupled to the low pass filter 18 and the band passfilter 19.

In operation, the method for enhancing bass effect in audio signals formono input in accordance with the third embodiment starts with the stepof extracting low frequency components 13 b from the mono input channel13 a using the low pass filter 18.

Passing the low frequency components 13 b from the mono input channel 13a through the exponential function block 30 is performed to generate anoutput signal 13 c.

The output signal 13 c undergoes filtering by the band pass filter 19.The band pass filter 19 limits the frequency from the output signal 13 cto a predetermined frequency range to produce a band filtered outputsignal 13 d.

The band filtered output signal 13 d is then added to the originalcontents of the mono input channel 13 a via mixer 24 producing aresultant output signal 13 e.

The resultant output signal 13 e is then sent as input to a mono inputchannel of audio speakers.

Sine Function Block

The Sine function block 20 transforms the input by passing it through asine wave transfer function. The input to this block are the outputs ofthe low pass filter 18 and hence consists of only low frequencycomponents of the audio signal. When the low frequency components of theaudio signal are passed through this sine function block 20, the outputof the sine wave transfer function will have frequency components whichare directly related to the input frequency components.

y(i)=sin(x(i))  Eqn. 1

Where, x is the input signal which is normalized and y is the outputnormalized signal.

Eqn. 1 given above shows the sine wave transfer function present in thisblock. The output vector y is basically derived after passing the inputvector x through a non linear sine wave transfer function.

Cosine Function Block

The Cosine function block 22 transforms input by passing it through acosine wave transfer function. The input to this block is the output ofthe low pass filter 18 and will consist of only low frequency componentsof the audio signal. When the low frequency components are passedthrough this cosine wave function block 22, the output of the cosinetransfer function will-have frequency components which are directlyrelated to the input frequency components.

y(i)=cos(x(i))  Eqn. 2

Eqn. 2 given above shows the transfer function present in this block.The output vector y is basically derived after passing the input vectorx through a non linear cosine wave transfer function.

Exponential Function Block

The Exponential function block 30 transforms input by passing it througha exponentially curved transfer function. The input to this block 30 isthe output of the low pass filter 18 and hence it consists of only lowfrequency components of the audio signal. When the low frequencycomponents of the audio signal are passed through this exponentialfunction block 30, the output of this block will have new frequencycomponents which are directly related to the input frequency components.

y(i)=exp(x(i))  Eqn. 3

Eqn. 3 given above shows the transfer function present in this block.The output vector y is basically derived after passing the input vectorx through a non linear exponentially saturating transfer function.

Initial Mixer Block

The initial mixer block 19 is responsible for mixing of the contents ofthe first input channel 15 a and the second input channel 16 a in thesecond embodiment. The initial mixer block 19 allows a user to controlthe percentage of the content of each input channel 15 a, 16 a in theresultant output signals 15 e, 16 e. The initial mixer block 19 mixesthe contents of the two input channels 15 a, 16 a weighted by weights w1and w2 as specified by the user. Eqn. 4 given below specifies how themixer channel output is obtained.

q(i)=w1*l(i)+w2*r(i)  Eqn. 4

Where, l(i) is the content in audio channel 1, r(i) is the content inaudio channel 2, and w1 and w2 are the user specified scaling factorssubjected to the constraint. And where,

w1+w2=1.  Eqn. 5

Simulations

A first simulation was performed using a simple 50 Hz sine wave as inputto both input channels 15 a, 16 a of the system 10, 30 of the first andsecond embodiment. Referring to FIG. 5, a frequency domain plot of theinput waveform is shown. Referring to FIG. 6 and FIG. 7 the frequencydomain plots of the resultant output waveforms of the system 10, 30 forthe resultant first output signal 15 e, 27 c and the resultant secondoutput signal 16 e, 29 c are shown respectively.

Referring to FIG. 5, the input waveform has only one component at 50 Hz.Referring to FIG. 6, the resultant first output signal 15 e, 27 ccomprises the original signal component at 50 Hz and the 2^(nd), 4^(th)and 6^(th) harmonics (even) of the input waveform.

Referring to FIG. 7, the resultant second output signal 16 e, 29 ccomprises of the original signal component at 50 Hz and the 3^(rd),5^(th) and 7^(th) harmonics (odd) of the input waveform.

A second simulation was performed using an input waveform containingfrequency components at 50 and 70 Hz as shown in FIG. 8. Referring toFIG. 9, the resultant first output signal 15 e, 27 c comprises theoriginal signal component at 50 Hz and 70 Hz together with frequencycomponents at 100, 120, 140, 160, 220, 140 and 160 Hz.

Referring to FIG. 10, a resultant second output signal 15 e, 27 ccomprises the original signal component at 50 Hz and 70 Hz together withfrequency components at 150, 170, 190, 210, 290 and 310 Hz.

A third simulation was performed using an input audio signal havingfrequency components at 50 Hz and 75 Hz for input into the system 60, 60a in accordance with the third embodiment.

Referring to FIG. 11, a frequency domain plot of the input audio signalis shown.

Referring to FIG. 6 and FIG. 7 the frequency domain plots of theresultant output waveforms of the system 10, 30 for the resultant firstoutput signal 15 e, 27 c and the resultant second output signal 16 e, 29c are shown respectively.

When this input audio signal is input to the exponential function block30, the output of the block is as shown in FIG. 12. It can be seen thatthe output has frequency components at 100 Hz (Harmonic of 50 Hz), 125Hz (75+50 Hz), 150 Hz (Harmonic of 75 Hz), 25 Hz (75−50 Hz) and theoriginal frequency components at 50 Hz and 75 Hz.

It can be seen that in response to the input signal which consisted of 2sinusoidal frequencies, the output comprises sinusoidal frequencies at25 Hz, 50 Hz, 75 Hz, 100 Hz, 125 Hz, 150 Hz and 175 Hz.

Some additional modifications for further improving on the describedembodiments are possible. For example, there may be the addition of oneor more high pass filters to the systems (e.g., 10, 30, 60, 60 a) toextract high frequency components of one or more input channels (e.g.,15 a, 16 a, 13 a) before adding one or more of them to the band filteredoutput signals (e.g., 15 d, 16 d, 27 b, 29 b, 35 a, 35 b, 13 d) tothereby produce resultant output signals (e.g., 15 e, 16 e, 27 c, 29 c,36, 37, 24).

Another exemplary modification includes adding an attenuator toattenuate the low frequency components (e.g., 15 b, 16 b, 13 b) of theinput channels (e.g., 15 a, 16 a, 13 a) before further processing.

It will be appreciated that although various embodiments have beendescribed in detail, additional modifications and improvements may bemade by a person skilled in the art without departing from the scope ofthe present invention.

1. A method for enhancing bass effect in audio signals, the audiosignals having a first input channel and a second input channel, themethod comprising: extracting low frequency components from the firstinput channel and the second input channel; passing the low frequencycomponents of the first input channel through a sine wave transferfunction to produce a first output signal; passing the low frequencycomponents of the second input channel through a cosine wave transferfunction to produce a second output signal; filtering the first outputsignal and the second output signal to produce a filtered first outputsignal and a band filtered second output signal; adding the filteredfirst output signal to the first input channel producing a resultantfirst output signal; and adding the filtered second output signal to thesecond input channel producing a resultant second output signal.
 2. Themethod of claim 1, wherein during filtering the first output signal andthe second output signal are limited to a predetermined frequency range.3. The method of claim 1, wherein the resultant first output signal andthe resultant second output signal are input to stereo speakers.
 4. Themethod of claim 1, wherein the sine wave transfer function isrepresented by:y(i)=sin(x(i)), where x is the input signal, which is normalized, and yis the output normalized signal.
 5. The method of claim 1, wherein thecosine wave transfer function is represented by:y(i)=cos(x(i)), where x is the input signal, which is normalized, and yis the output normalized signal.
 6. The method of claim 1, whereinadding the filtered first output signal to the first input channelfurther comprises extracting high frequency components of the firstinput channel and adding the high frequency components to the filteredfirst output signal.
 7. The method of claim 1, wherein adding thefiltered second output signal to the second input channel furthercomprises extracting high frequency components of the second inputchannel and the adding the high frequency components to the filteredsecond output signal.
 8. The method of claim 1, wherein extractingfurther comprises attenuating the low frequency components of the firstinput channel and the second input channel.
 9. A system for enhancingbass effect in audio signals, the audio signals having a first inputchannel and a second input channel, comprising: a first low pass filterconfigured to receive signals from the first input channel; a second lowpass filter configured to receive signals from the second input channel;a sine function block coupled to an output of the first low pass filterand configured to produce a first output signal; a cosine function blockcoupled to an output of the second low pass filter and configured toproduce a second output signal; a filter configured to limit thefrequency range of the first output signal and the second output signaland produce a filtered first output signal and a filtered second outputsignal.
 10. The system of claim 9 further comprising a high pass filterconfigured to extract high frequency components of the first inputchannel and the second input channel.
 11. The system of claim 10 furthercomprising an adder configured to add extracted components to thefiltered first output signal and the filtered second output signal. 12.The system of claim 9 further comprising an input source configured toreceive the first and second output signal.
 13. The system of claim 12,wherein the input source is stereo speakers.
 14. The system of claim 9further comprising an attenuator configured to attenuate the lowfrequency components of the first input channel and the second inputchannel.
 15. A method for enhancing bass effect in audio signals, theaudio signals having a first input channel and a second input channel,the method comprising: extracting low frequency components from thefirst input channel; extracting low frequency components from the secondinput channel; passing the low frequency components of the first inputchannel through a sine wave transfer function; passing the low frequencycomponents of the second input channel through a cosine wave transferfunction; bandpass filtering the first output signal to produce a bandfiltered first output signal; bandpass filtering the second outputsignal to produce a band filtered second output signal adding the bandfiltered first output signal to the first input channel producing aresultant first output signal; and adding the band filtered secondoutput signal to the second input channel producing a resultant secondoutput signal.
 16. The method of claim 15, wherein adding the bandfiltered first output signal to the first input channel furthercomprises extracting high frequency components of the first inputchannel and adding the high frequency components to the band filteredfirst output signal.
 17. The method of claim 15, wherein adding the bandfiltered second output signal to the second input channel furthercomprises extracting high frequency components of the second inputchannel and the adding the high frequency components to the bandfiltered second output signal.
 18. The method of claim 15, whereinextracting low frequency components from the first input channel furthercomprises attenuating the low frequency components of the first inputchannel.
 19. The method of claim 15, wherein extracting low frequencycomponents from the second input channel further comprises attenuatingthe low frequency components of the second input channel.
 20. The methodof claim 15, wherein the sine wave transfer function is represented by:y(i)=sin(x(i)) where, x is the input signal which is normalized; and yis the output normalized signal.
 21. The method of claim 22, wherein thecosine wave transfer function is represented by:y(i)=cos(x(i)) where, x is the input signal which is normalized; and yis the output normalized signal.
 22. A system for enhancing bass effectin audio signals, the audio signals having a first input channel and asecond input channel, the system comprising: a low pass filterconfigured to receive the first and second input channels and extractlow frequency components of the first and second input channels; a firstcircuit configured to pass each of the low frequency components of thefirst and second input channels through a sinusoidal wave transferfunction to produce a first output signal and a second output signal; aband pass filter configured to limit frequency range of the first outputsignal and the second output signal to a predetermined frequency rangeand respectively produce a band filtered first output signal and a bandfiltered second output signal; a second circuit configured to add theband filtered first output signal to the first input channel; and athird circuit configured to add the band filtered second output signalto the second input channel.
 23. The system of claim 22, wherein thefirst circuit includes a sine function block configured to receive lowfrequency components of the first input channel and produce the firstoutput signal and a cosine function block configured to receive lowfrequency components of the second input channel and produce the secondoutput signal.
 24. The system of claim 22 further comprising at leastone a high pass filter configured to extract high frequency componentsof the first input channel and the second input channel before additionto the band filtered first output signal and the band filtered secondoutput signal.
 25. The system of claim 22 further comprising at leastone attenuator configured to attenuate the low frequency components ofthe first input channel and the second input channel.
 26. The system ofclaim 23, wherein the sine function block is represented by:y(i)=sin(x(i)), where x is the input signal, which is normalized, and yis the output normalized signal.
 27. The system of claim 23, wherein thecosine function block is represented by:y(i)=cos(x(i)), where x is the input signal, which is normalized, and yis the output normalized signal.
 28. A method for enhancing bass effectin audio signals, the audio signals having input channels, the methodcomprising: extracting low frequency components from the input channels,wherein content of each input channel is not independent; passingextracted low frequency components through sinusoidal wave transferfunctions; filtering the extracted low frequency components; mixing theextracted low frequency components; wherein for each input channeloperations are performed separately.
 29. The method of claim 1, whereinextracting includes low pass filtering each input channel separately.30. The method of claim 28, wherein mixing comprises separately mixingfiltered output of each input channel with original signals feeding intoeach input channel.
 31. The method of claim 28, wherein during operationoutput from each input channel remains separate.
 32. The method of claim28 further comprising providing resultant output signals to inputchannels of at least one audio speaker.
 33. The method of claim 28,wherein extracting low frequency components from each input channeloccurs simultaneously.
 34. The method of claim 28, wherein the inputchannels are stereo channels.
 35. The method of claim 28, whereinsinusoidal wave transfer functions include a sine wave transfer functionfor at least a first input channel and a cosine wave transfer functionfor at least a second input channel.